Multicolor dental blanks and related methods

ABSTRACT

A dental blank has at least an inner zone (or layer) of a first color and an outer zone (or layer) of a second color, wherein the inner and outer zones are concentric. The inner zone can be surrounded in its entirety by the outer zone such that only the outer zone is visible on all surfaces of the blank. Alternatively, the inner zone and the outer zone can extend to a same single surface of the blank, such that only the outer zone covers all remaining surfaces. The blank may also have an intermediate zone between the inner and outer zones. A method of fabrication includes solid free form processes, such as robocasting, laser sintering and 3D printing that allow for placement of multiple colors. A dental restoration made from the blank can have a variety of shades depending on a ratio of milled outer layers to internal layers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/934,618 entitled MULTICOLOR DENTAL BLANKS AND RELATED METHODS, filedSep. 24, 2010, which is a National Stage Application ofPCT/US2007/089157, filed Dec. 28, 2007, which claims priority to and thebenefit of U.S. provisional application No. 60/878,041, filed Dec. 28,2006, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to methods and materials for machinable multicolordental blanks to fabricate polychromatic, color-graded dental deviceswhich replicate the color gradation of natural teeth.

BACKGROUND OF THE INVENTION

Presently, dental blanks are composed of a single color, or of multiplecolors layered on top of each other. The monochromatic blocks may notmatch the natural color gradation found in natural teeth. Furthermore,shades of these colored blocks are limited in number, and may not evenmatch an overall base shade of a tooth.

One known type of block does have three layers of color. However, theselayers extend fully to surfaces of the block, and result in restorationswith sharp gradations in color, as opposed to natural teeth which havegradual changes in color. Furthermore, natural teeth have colorgenerated internally by overlapping colors from the enamel and dentin ofthe tooth.

Conventional methods of fabricating dental blocks involve pressingpowders into a mold or using an extrusion from which blocks are thenfired to full density. These are time and labor intensive processes anddo not easily allow for placement of multiple colors as desirable fordental blocks with improved color matching.

Accordingly, it would be desirable to provide a blank with color zoneswhich correspond to colors found in natural teeth. Moreover, it would bedesirable to provide a blank from which restorations with varying ratiosof color thicknesses can be produced. It would also be desirable toprovide a method of fabrication of dental blocks that readily allows forplacement and incorporation of multiple colors.

SUMMARY OF THE INVENTION

The proposed blank has concentric zones of color which correspond tocolors found in natural teeth. A restoration may be positioned in theblank to produce a milled restoration with layered overlapping colors.The resulting milled restoration more closely resembles the layeringfound in natural teeth. Furthermore, the restoration may be positionedin the blank to produce varying ratios of color thickness which allowsfor production of multiple shades from a single blank. Blocks currentlyon the market are a single shade, or are limited in the number of shadesavailable. The proposed blank would allow for more shades to beproduced, and thus improve the likelihood of a match to the patient'snatural dentition.

In one embodiment, a dental blank of the present invention has at leastan inner zone of a first color and an outer zone of a second color,wherein the inner and outer zones are concentric. The inner zone can besurrounded in its entirety by the outer zone such that only the outerzone is visible on all surfaces of the blank and the inner zone is notvisible on any surface of the blank. Alternatively, the inner zone andthe outer zone can extend to a same single surface of the blank, suchthat only the outer zone covers all remaining surfaces.

In a more detailed embodiment, the inner zone has a first chroma and theouter zone has a second chroma, wherein the first chroma is greater thanthe second chroma, or the color of the inner zone is darker than thecolor of the second zone.

In another embodiment, the dental blank has an intermediate zone betweenthe inner and outer zones. The intermediate zone can be surrounded inits entirety by the outer zone and/or the intermediate zone surroundsthe inner zone in its entirety, or the intermediate zone can extend tothe same single surface of the blank to which the inner and outer zonesextend.

The dental blank may have a generally rectangular configuration or agenerally cylindrical configuration. The zones may have a generallyrectangular configuration or a generally cylindrical configuration,wherein the configuration of the zones is independent of theconfiguration of the blank. Some or all of the zones may also have thesame thickness or different thicknesses.

In another detailed embodiment, the invention comprises a blank ofconcentric polychromatic (typically three or more colors) material. Theblank is composed of porcelain, ceramic, glass, glass ceramic, compositeresin, acrylic, or other machinable or heat-pressable material. Aholder, if needed, of metal, plastic, or a combination of thesematerials may be glued directly on the blank, or the blank may be moldeddirectly on the holder for placement in a milling device.

The present invention also includes fabrication of dental blanks throughsolid free form processes, such as robocasting, laser sintering and 3Dprinting that readily allow for placement of multiple colors in a singledental blank. A method of manufacturing a dental blank includes solidfree form fabricating a dental blank having at least a first and asecond concentric zones, wherein the first concentric zone has one colorand the second concentric zone has another color. The solid free formfabrication can be robocasting, three dimensionally printing or lasersintering. In a more detailed embodiment, the solid free formfabricating a dental blank includes providing a depositing deviceadapted to deposit a material of a first color and a material of asecond color, providing a platform, wherein the depositing device andthe platform move in a predetermined pattern relative to each other, andcontrolling the depositing device to switching between depositing thematerial of the first color and depositing the material of the secondcolor. The predetermined pattern can be a spiral, a raster, orvariations or combinations thereof.

The methods and materials for producing milled dental devices of thepresent invention can overcome shortcomings of prior-art devices. Themethods and materials for producing dental blanks of the presentinvention can be applied to fabricate polychromatic, color-graded dentaldevices which replicate the color gradation of natural teeth. Themethods and materials for producing dental blanks of the presentinvention can also allow for the production of a variety of shades froma single block of material by varying the ratio of milled outer layersto internal layers.

DETAILED DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bebetter understood by reference to the following detailed descriptionwhen considered in conjunction with the accompanying drawings wherein:

FIG. 1. is a perspective view of one embodiment of a dental blank of thepresent invention.

FIG. 1A is a perspective view of the dental blank of FIG. 1 showingconcentric zones.

FIG. 2 is a top view of the dental block of FIG. 1.

FIG. 2A is a cross-sectional view of the dental block of FIG. 2 takenalong line A-A.

FIG. 3 is an end view of the dental block of FIG. 1.

FIG. 4 is a side elevational view of the dental block of FIG. 1, withrestoration contour lines C1, C2 and C3.

FIG. 5 is perspective view of another embodiment of a dental blank ofthe present invention.

FIG. 6 is a top elevational view of the dental blank of FIG. 5.

FIG. 6A is a cross-sectional view of the dental blank of FIG. 6, takenalong line A-A.

FIG. 7 is an end view of the dental blank of FIG. 6.

FIG. 8 is a top view of the dental blank of FIG. 6, showing arestoration contour line C.

FIG. 9 is a side view of another embodiment of a dental blank showingconcentric zones with different configurations and/or thicknesses.

FIG. 10 is a perspective view of another embodiment of a dental blank ofthe present invention, whose internal concentric zones do not extend anysurface of the dental blank.

FIG. 10A is a perspective view of the dental blank of FIG. 10 showingconcentric zones.

FIG. 11 is a top view of the dental block of FIG. 10.

FIG. 11A is a cross-sectional view of the dental block of FIG. 11 takenalong line A-A.

FIG. 12 is a side elevational view of the dental block of FIG. 10.

FIG. 13 is an end view of the dental block of FIG. 10.

FIG. 14 is a top view of the dental block of FIG. 10, showing arestoration contour line C′.

FIG. 15 is a cross sectional view of an embodiment of a milled dentalblock of the present invention.

FIG. 16 is a top view of yet another embodiment of a dental block of thepresent invention.

FIG. 16A is a cross sectional view of the dental block of FIG. 16, takenalong line A-A.

FIG. 17 shows a schematic representation on an embodiment of a system inaccordance with the present invention.

FIG. 18 shows a perspective view of an embodiment of a cylindrical blankas fabricated in accordance with the present invention.

FIG. 19 shows a perspective view of an embodiment of a rectangular blankas fabricated in accordance with the present invention.

FIG. 20 shows a perspective view of an embodiment of a rectangular blankas fabricated in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A blank in accordance with the present invention is composed ofporcelain, ceramic, glass, glass ceramic, acrylic, composite resin, acombination of some of these materials, or other materials withconcentric colors representing natural tooth colors. Colorants may beinorganic or organic. A suitable porcelain may be composed of a varietyof materials with a glass matrix such as feldspathic glasses, silica,aluminosilicates, and crystalline materials such as leucite,fluorapatite, fluoromica, with other metallic oxides as colorants ormatrix/crystal components. Ceramic materials may include metallic oxidessuch as alumina, zirconia, spinel or other monocrystalline orpolycrystalline materials. As understood by one of ordinary skill in theart, ceramics and porcelains may contain inorganic colorants to achievethe proper color gradation to match natural teeth. Moreover, acrylic andcomposite resins may be composed of methacrylates such as methylmethacrylate or urethane dimethacrylate, BIS-GMA, epoxies,polyacrylamide, with or without glass, ceramic, or fibers commonly usedas fillers for direct or indirect resin-based restorative materials.

As illustrated in FIGS. 1-14, a blank (or block, used interchangeablyherein) B of the present invention may be in the form of a cylinder ofvarious diameters and lengths, or a rectangle of various dimensions,e.g., widths, lengths and heights. In any of these forms, the blank hasat least two opposing surfaces S1 and S2. In the case of a rectangularblank BR (inclusive of a square blank) as illustrated in FIGS. 1-4,there are the opposing surfaces S1 and S2 with four additional surfacesS3-S6 extending therebetween. In the case of a cylindrical blank BC asillustrated in FIGS. 5-8, there are the opposing surfaces Si and S2 anda tubular surface ST extending therebetween.

In accordance with a feature of the present invention, the blank Bwhether it is cylindrical or rectangular (or any other shape) isconfigured with a plurality of concentric zones (or layers) of colorsZ1, Z2, . . . Zn, with the plurality n ranging between about 2 to 5, andmore preferably about 3. The zones may be of varyingsizes/volumes/thicknesses, and varying degrees of chroma, hue and value.Typically two or three zones of color extend from darker to lighter,and/or higher chroma to lower chroma, as one proceeds from an innermostor internal zone Z1, to middle or intermediate zone(s) Zi and to anoutermost or external zone Zn.

In one embodiment of the blank, all of the concentric zones extend toone of the surfaces S1 or S2, such that all of the concentric zones arevisible on that one surface only. In the embodiment of FIGS. 5-8, all ofthe concentric zones Z1-Z3 of the cylindrical blank BC are visible onsurface S1, whereas only the outermost zone Z3 is visible on theremaining surfaces S2 and ST. In the embodiment of FIGS. 1-4, all of theconcentric zones Z1-Z3 of the rectangular blank BR are visible onsurface S1, whereas only the outermost zone Z3 is visible on theremaining surfaces S2, and S3-S6.

It is understood by one of ordinary skill in the art that with eitherthe blank BC or BR, each of the surfaces except for the surface on whichthe concentric zones are visible (namely S1 in the illustratedembodiments) presents a surface underneath which the different zonesZ1-Zn are layered to advantageously simulate the layering structurefound in natural teeth. The concentric zones and colors are containedwithin the block, with outwardly decreasing chroma, and with possibledifferences in shade and opacity. The change in chroma progresses froman internal layer Z1, through an intermediate layer Zi, to an externallayer Zn. In accordance with a feature of the present invention, aresulting color and chroma that is visible on the surfaces on which onlythe outermost zone Zn is visible (namely, all surfaces except for thesurface S1) is composed of a combination of the colors and chromas ofall the zones layered below the surfaces of the blank.

In another embodiment, only the outer zone Zn extends to the surfaces ofthe blank. As illustrated in FIGS. 10-13, the innermost zone Z1 issurrounded entirely by the intermediate zone Z2, which in turn issurrounded entirely by the outermost zone Z3. Accordingly, only theoutermost zone Z3 is visible on all surfaces of the blank. In accordancewith a feature of the present invention, the color and chroma visible onall of the surfaces of the blank is a combination of all the colors andchromas of all the zones that are layered under the surfaces of theblank.

In the illustrated embodiments of FIGS. 1-8 and 10-13, the zones have across section or overall shape that mirrors the cross section or overallshape of their respective blank. That is, the zones of the rectangularblank BR have a generally rectangular shape and the zones of thecylindrical blank BC have a generally cylindrical shape. Conceivably,the zones may not mirror the shape of their respective blank, and acylindrical blank can have rectangular zones, and a rectangular blankcan have cylindrical zones, or a blank can even have a mix ofrectangular or cylindrical zones as appropriate or desired.

Moreover, the zones within a blank can have the same or differentthicknesses, and the thickness of any one zone can also be varied indifferent dimensions, for example, in the (X,Y,Z) Cartesian coordinates,or (R, Z) polar coordinates. In the illustrated embodiments, the zonesZ2 and Z3 of the block BR are generally thicker than the zone Z1, andthe zone Z2 of Block BC is thinner than both zones Z1 and Z3. Asillustrated in FIG. 9, the block whether it is a rectangular block BR ora cylindrical block BC, a zone (such as zone Z2) can have a greaterthickness in one dimension (e.g., X axis) and a lesser thickness inanother dimension (e.g., Y axis).

Furthermore, the zones within a blank may be varied in whether theyextend to a surface of the blank. As illustrated in FIGS. 16 and 16A,the zone Z1 may be surrounded entirely by zone Z2 and not extend to anysurface of the blank, but the zone Z2 may extend to the surface S1.Indeed, any variation in the configuration or the thickness of the zonesis contemplated within the present invention, as desired or appropriate.However, in accordance with a feature of the present invention, thezones remain generally concentric.

The blank may be made partially or completely opaque, and may be coloredto match natural tooth colors or other colors. Additional materials maybe added to the milled devices to further alter color or shape. Theblank may be positioned in a milling device to alter a ratio of milledexternal colors to internal colors to produce multiple tooth shades froma single blank.

The blank may be used directly as a final or provisional restoration.The blank may be milled to provide a substructure for other materialslayered on the milled blank to produce a final or provisionalrestoration.

In one embodiment, a porcelain blank is placed in a spindle of a millingdevice. The blank is milled to form a full-contour dental restoration,using computer design and milling. A proper blank is selected for thetooth color being matched, and is placed in the milling system. Theblank is milled to provide an inner layer(s) of darker, more chromaticmaterial, with an outer layer(s) of lighter, less chromatic material.This replicates the gradation in color found in the tooth beingrestored, and in the adjacent natural teeth. In the illustratedembodiments, the innermost layer Z1 provides the darker, more chromaticmaterial and the outermost layer Zn provides the lighter, less chromaticmaterial.

A holder H comprised of metal, plastic or a combination thereof, may beattached to the blank for placement in the milling device. The holdermay be glued to the blank, or the blank may be directly processed on theholder. The holder H may be fixed to the block in order to facilitatepositioning in the milling device. This may or may not be necessary, andthe holder is not limited to the exact configuration as illustrated.Referring to FIG. 4, the block may be milled to produce a full-contourrestoration, such as a crown C. The layers Z1, Z2 and Z3 represent thenatural layering of color seen in a tooth. An outline of the crown C1 isshown in FIG. 4. Notably, the surface S1 on which all zones of the blankare visible coincides with a bottom of the crown C1, that is, a surfacefor which there is minimal need for matching color with natural teeth.Correspondingly, all other surfaces of the crown C1 lie in an areaunderneath which is a layering of the various zones of the blank. And,by adjusting the outline of the crown C1 in FIG. 4, the thickness of theoutermost zone Z3 at any region can be varied so as to vary theresulting color/chroma in that region. For example, where the outline islowered to C2, the crown has a thinner layer of Z3 on its biting orocclusal surface. And, where the outline is raised to C3, the crown hasa thicker layer Z3 on its occlusal surface. Similarly, a shift to theleft or right in FIG. 4, can result in the crown having a thinner orthicker layer of Z3 on its facial or lingual surface. Since a differencein the thickness of the layer of Z3 can affect color/chroma, the crownfollowing outline C2 has a different color/chroma from the crownsfollowing outlines C1 and C3. However, all crowns C1, C2 and C3 have thebenefit of a more natural looking color/chroma resulting from thelayering effects of zones Z1, Z2 and Z3.

FIGS. 10-13 illustrate another embodiment of a multicolor rectangularbank BR′ (although it is understood that the following descriptionapplies to a cylindrical blank). In this embodiment, the inner zones orlayers are surrounded in their entirety by the outer zones or layers sothat only the outermost zone Zn (in this instance Z3) is visible on thesurface S1. Also in this embodiment, the chroma decreases from aninternal layer Z1, to an intermediate layer Z2, and then is lowest at anouter layer Z3. Furthermore, as with the previous embodiments, theopacity and color may also change. FIG. 14 illustrates a full-contourcrown fabricated using this block embodiment block. An outline C′ of thecrown is depicted. Again, it is understood that by adjusting theplacement of the outline C′, the thickness of the layer of Z3 can beincreased or decreased in all three dimensions of X, Y and Z.

FIG. 15 illustrates one embodiment of a milled full-contour crown inwhich three layers of increasing chroma have been used. As illustrated,each zone Z1-Z3 has a similar configuration resembling that of the crownor the resulting dental device/prothesis. A lower-central area 23contains no material, and fits on a mating portion of a prepared tooth.Chroma outwardly decreases from an inner layer or zone Z1 (highestchroma) through a middle layer or zone Z2, to an outer layer or zone Z3(lowest chroma). Shade and opacity may also be varied across theselayers. Furthermore, varying the thickness ratio of the three layers)may allow fabrication of a variety of tooth shades from a single block.

Regardless of the specific embodiment of a blank, a method of milling adental prosthesis from the blank can include using a blank withconcentric zones of different colors, including an outermost zone, andpositioning a form of the dental prosthesis on the blank wherein anocclusal surface of the prosthesis is contained in the outermost zone,so that the occlusal surface provides a resulting color/chroma thatresults from the combination of colors/chromas of the underlying zones.And, by adjusting the positioning of the form on the blank, theresulting color/chroma can be adjusted.

Advantageously, position of the block may be altered in the millingsystem to allow for improved color replication and production ofmultiple tooth shades from a single block.

Alternatively, the blank may be milled to provide a substructure uponwhich additional colored layers may be applied to produce the finaldental restoration.

Alternatively, the above procedures may be followed to produce aprovisional restoration.

Alternatively, the blank may be milled to produce a superstructure,which is then joined to a substructure by gluing or firing, using anintermediary glass, porcelain or ceramic material.

Alternatively, the blank may be milled to produce a denture tooth.

Alternatively, the blank may be heated until flowable, and pressed ormolded into a tooth pattern to fabricate the dental restoration.

The multicolor layered blank may be fabricated by sequential pressing,injection molding, or three-dimensional rapid manufacturing techniques.These include selective laser sintering, three-dimensional printing, orRobocasting/Direct slurry deposition, or deposition of a suspension ofthe component materials.

Selective Laser Sintering is an additive rapid manufacturing techniquethat uses a high power laser (for example, a carbon dioxide laser) tofuse small particles of plastic, metal, or ceramic powders into a massrepresenting a desired 3-dimensional object. The laser selectively fusespowdered material by scanning cross-sections generated from a 3-Ddigital description of the part (e.g. from a CAD file or scan data) onthe surface of a powder bed. After each cross-section is scanned, thepowder bed is lowered by one layer thickness, a new layer of material isapplied on top, and the process is repeated until the part is completed.

Three-dimensional printing is a method of converting a virtual 3D modelinto a physical object. 3D printing is a category of rapid prototypingtechnology. 3D printers typically work by printing successive layers ontop of the previous to build up a three dimensional object.

Robocasting is a method of fabricating ceramics that requires no moldsor machining, by generally relying on robotics for computer-controlleddeposition of ceramic slurries—mixtures of ceramic powder, water, andtrace amounts of chemical modifiers—through a syringe. The material,which flows like a milkshake even though the water content is only about15 percent, is deposited in thin sequential layers onto a heated base.The product manufactured is fabricated layer by layer by a robot thatsqueezes a slurry out of the syringe, following a pattern prescribed bycomputer software. A suitable robocasting method is described in U.S.Pat. No. 6,027,326, and 6,401,795, the entire disclosures of which arehereby incorporated by reference.

The foregoing techniques and other types of solid free form fabricationallow for placement of multiple colors. As illustrated in FIG. 17, anembodiment of a system S for freeforming a dental blank includes amoveable platform 100 and a material depositing device 120 having anozzle or printer head 124 through which material (e.g., a slurry 1) 130is controllably deposited. Conventional means are provided forcontrollably moving depositing device 120 with respect to platform 110in at least X, Y, and Z directions. As illustrated, platform 110 may bean X-Y table which is moveable in the X-Y plane by a platform controller132, and device 120 may be driven by conventional means, such as athreaded rod in the Z direction. Alternatively, platform 110 may befixed and device 120 may be affixed to a robotic arm moveable in anydirection. In addition, both platform 110 and device 120 may be moveablewith respect to one another.

Depositing device 120 may be a syringe or a printer head. The movementof device 120 with respect to platform 110, and actuation of thedepositing device 120, is controlled by a programmed processor orcomputer 140.

To provide the different zones of colors in the blank B, the S system inthe illustrated embodiment includes a color or pigment source 160 thatis also connected to the processor 140 which controls the amount ofcolor or pigment to be mixed with the slurry 1. Alternatively, thesystem can include a second material 130′ (e.g., slurry 2 with adifferent color, shade or chroma,) which the processor 140 can select asan alternate source of material for the depositing device 120.

With further reference to FIG. 18, in fabricating a cylindrical blankBC, the relative movement between the platform and the depositing device120 may be a spiral pattern (illustrated in broken lines) that isgenerally circular. The spiral can be inwardly and/or outwardly,creating layer upon layer of material with each pass over the samelocation on the blank. In one embodiment, where the blank BC has aninner zone Z1 and an outer zone Z2, the computer 140 starts a depositionprocess by positioning the depositing device at location A anddepositing the slurry II from the material source 130′ in an inwardlyspiral counterclockwise pattern to begin creating the zone Z2. When thedepositing device reaches a boundary or border 200 between the zones Z1and Z2, the computer 140 changes the amount of color or pigment from thesource 160 to be added to the slurry II to begin creating the zone Z1.The deposition process in the zone Z1 continues until the depositingdevice reaches location B (e.g., a center of the blank), at which stagethe computer 140 can reverse the deposition pattern to an outwardlyspiral clockwise pattern to add another layer to the zone Z1. When thedepositing device again reaches the boundary 200, the computer 140changes the amount of color back to that used for the zone Z2.Alternatively, when the deposition device reaches the boundary 200, thecomputer 140 can switch the source of the slurry for the depositiondevice between materials 130 and 130′ for building the zones Z1 and Z2,respectively. It is understood that while the embodiment of FIG. 18shows the relative movement between the nozzle and the platform as aspiral pattern, the pattern can also be a raster (see FIG. 20), althoughthe frequency in changing the amount of color/pigment input from thecolor source 160, or in switching between the material sources 130 and130′ would be greater. With reference to FIG. 19, a generallyrectangular blank BR can be fabricated with a relative pattern that isgenerally rectangular. Indeed, the relative pattern can also correspondwith or be dependent on the configurations of the zones.

The preceding description has been presented with reference to presentlypreferred embodiments of the invention. Workers skilled in the art andtechnology to which this invention pertains will appreciate thatalterations and changes in the described structure may be practicedwithout meaningfully departing from the principal, spirit and scope ofthis invention.

Accordingly, the foregoing description should not be read as pertainingonly to the precise structures described and illustrated in theaccompanying drawings, but rather should be read consistent with and assupport to the following claims which are to have their fullest and fairscope.

What is claimed is:
 1. A dental blank comprising at least an inner zoneof a first color and an outer zone of a second color, wherein the innerand outer zones are concentric, and the dental blank has a geometricshape, wherein the inner zone is surrounded in its entirety by the outerzone such that only the outer zone is visible on all surfaces of theblank and the inner zone is not visible on any surface of the blank,wherein each zone has generally the same geometric shape, and whereinthe blank has multiple outer surfaces, each of which has a resultingcolor that is of a combination of at least the first color of the innerzone and the second color of the outer zone.
 2. The dental blank ofclaim 1, wherein the inner zone has a first chroma and the outer zonehas a second chroma.
 3. The dental blank of claim 2, wherein the firstchroma is greater than the second chroma.
 4. The dental blank of claim1, wherein the first color is darker than the second color.
 5. Thedental blank of claim 1, further comprising an intermediate zone betweenthe inner and outer zones.
 6. The dental blank of claim 1, furthercomprising an intermediate zone surrounded in its entirety by the outerzone.
 7. The dental blank of claim 1, further comprising an intermediatezone, wherein the inner zone is surrounded in its entirety by theintermediate zone.
 8. The dental blank of claim 1, further comprising anintermediate zone between and concentric with the inner and outer zones.9. The dental blank of claim 1, wherein the blank has a generallyrectangular configuration.
 10. The dental blank of claim 1, wherein theblank has a generally cylindrical configuration.
 11. The dental blank ofclaim 1, further comprising a holder.